The membrane distillation (MD) technology controls temperature gradients of fluids at two sides of a membrane to form a vapor pressure difference. An aqueous solution containing salt enters a high temperature side of the membrane to form water vapor. The water vapor is driven by the vapor pressure difference to transfer to a low temperature side of the membrane through membrane pores, and is then condensed to a liquid. As such, the salt is kept at the high temperature side of the membrane, thereby separating the water from the salt. The MD membrane material should simultaneously have high porosity and hydrophobic property, e.g. PVDF. For preparing conventional porous PVDF membranes, a pore creating agent should be added to tune a phase transfer mechanism between a coagulant (e.g. water) and a solvent for achieving the porous requirement when the PVDF membrane is shaped. The pore creating agent is generally an ionic compound, surfactant, hydrophilic polymer, or the like with different shortcomings. If the ionic compound or the hydrophilic polymer serves as the pore creating agent of the hydrophobic polymer membrane, the hydrophobic property of the polymer membrane will be reduced. If the surfactant serves as the pore creating agent of the hydrophobic polymer membrane, pores that are too large will be formed in the membrane.
Accordingly, a novel pore creating agent is called for for preparing a hydrophobic porous membrane to be applied in the MD.